The present invention is directed toward a traffic light dimmer system and more particularly toward a system which reduces the power to traffic lights as the ambient light intensity decreases, i.e. during the nighttime hours. The system also includes a means for monitoring itself and bypassing the reduction circuit thereby providing full power to the lights in the event of a failure in the reduction circuit components.
It is well known in the art that the intensity of traffic lights may be substantially reduced during periods of darkness without sacrificing the proper visability of the traffic lights for safety purposes. It is also known that significant amounts of energy can be saved by reducing the amount of power to traffic lights during periods of darkness. Circuits for reducing power to traffic lights are shown, for example, in U.S. Pat. Nos. 3,500,455; 3,500,456; and 3,885,197.
While the circuits described in the foregoing patents may be somewhat effective, they all suffer from the same serious drawback. In the event of a failure in the components which actually reduce the power to the traffic lights, it is possible that all power to the traffic lights will be removed thereby disabling the lights. U.S. Pat. No. 3,885,197 does recognize this problem and attempts to provide some solution thereto. However, the solution is not satisfactory.
The circuit described in U.S. Pat. No. 3,885,197 includes a power switch means which is normally closed thereby allowing full power to pass to the traffic lights. When a photocell senses a reduction in the ambient light, the power switch means is caused to periodically open thereby effectively reducing the power to the traffic lights. The patent suggests that this is a fail safe means since, with the switch normally closed, 100 percent of the power will be delivered to the traffic lights in the event that the dimmer circuit is not operating properly. The patent, however, overlooks the possibility that the circuit could malfunction in such a manner to cause the power switch means to remain open. This would cause the traffic lights to turn off and remain off. The patented circuit cannot protect for this type of malfunction.